The invention relates generally to electrical discharge machining.
More particularly, the invention relates to the automatic control of electrical discharge machining.
Automatic control of electrical discharge machining is used to accelerate the erosion process and to increase the machining accuracy. It is further useful in preventing damage to components of complicated shape and components consisting of conductive materials which are difficult to machine.
Conventional automated control methods employ input signals which do not contain sufficient information to completely exclude electrode damage.
A method of automatically controlling electrical discharge machining of metals and alloys is known from the Swiss patent 647180. In this method, the amplitude of the alternating component of the electrical resistance in the gap defined by the machining electrode and the workpiece electrode, i.e., the electrode consisting of the metal or alloy to be machined, is periodically measured. The measurements are carried out during the pauses of uniform duration and frequency occurring between groups of electrical discharges. The amount of working fluid delivered to the machining zone is varied in dependence upon the results of the measurements.
In those cases where rinsing of the working fluid can be performed, the preceding method makes it possible to optimize the consumption of working fluid.
The modern tendency in the drain erosion process, however, is to manufacture relatively complicated articles without rinsing of the working fluid. Here, adaptive variations in current and regulation of the electrode spacing are the most important controls and provide the quickest response to changes in the process.
The method outlined above does not permit such a rapid response to be achieved. Thus, for effective analysis, it is necessary to have many measurements which are proportional to the amplitude of the alternating component of the electrical resistance in the gap defined by the electrodes.
The method described earlier also does not allow timely corrections in current to be realized because the duration of the pauses between groups of discharges is not regulated.